1. Field of the Invention
The present disclosure relates to a heat storage material composition and a method for using a heat storage material composition.
2. Description of the Related Art
In the case where thermal energy is used for industrial or domestic purposes, the amount of thermal energy used or the timing at which thermal energy is to be used is often different from the amount of thermal energy generated or the timing at which thermal energy is generated. Therefore, in order to effectively utilize all the heat that has been generated, the use of a medium that temporarily stores thermal energy, that is, a so-called “heat storage material”, has been proposed.
Heat storage materials are broadly divided into sensible heat storage materials and latent heat storage materials. Latent heat storage materials utilize a phase change such as fusion of a substance. Latent heat storage materials are advantageous in that a temperature at which heat is extracted is stable because the thermal storage density is higher than that of sensible heat storage materials and a phase-change temperature is constant. Accordingly, latent heat storage materials have been practically used. Heat storage using a latent heat storage material is performed as follows. In the case where heat is stored, the latent heat storage material is heated so as to be in a liquid state. Subsequently, the latent heat storage material is preserved while the temperature is maintained so as to maintain the liquid state. Heat stored in the preserved latent heat storage material can be extracted by crystallizing (coagulating) the latent heat storage material when needed.
Among such latent heat storage materials, sodium acetate trihydrate has a relatively large latent heat of fusion and thus is known as a substance that can efficiently store heat with a small volume. Sodium acetate trihydrate does not exhibit toxicity and is a safe substance. For example, Japanese Unexamined Patent Application Publication No. 2008-20177 (Patent Literature 1) discloses a system in which sodium acetate trihydrate is used as a heat storage material. Japanese Patent No. 5013499 (Patent Literature 2) discloses that sodium acetate trihydrate is used in a slurry for transportation of latent heat, the slurry being used in thermal equipment or the like.
The following is known about sodium acetate trihydrate. At the time of fusion, sodium acetate trihydrate is fused at a temperature (melting point) that is intrinsic to the substance. However, at the time of coagulation, sodium acetate trihydrate does not coagulate and is in a so-called supercooled state (supercooled liquid state) even at a temperature lower than the melting point.
Consequently, it has been proposed that sodium acetate trihydrate be used as a heat storage material, and the heat storage material that has been heated and has been in a liquid state be preserved in the supercooled state. At the time of heat dissipation, heat stored in the heat storage material can be extracted by breaking the supercooled state.
A heat storage material composition whose stability of the supercooled state can be enhanced, the composition being used in such a method for storing heat utilizing the supercooled state, has been proposed. For example, Japanese Unexamined Patent Application Publication No. 61-9484 (Patent Literature 3) has proposed a heat storage material composition obtained by adding salt-resistant carboxymethyl cellulose to sodium acetate trihydrate. Patent Literature 3 further describes that this heat storage material composition in the supercooled state can be stably preserved in an environment at room temperature. Japanese Unexamined Patent Application Publication No. 4-324092 (Patent Literature 4) has proposed a heat storage material composition obtained by adding 10% to 30% by weight of pure water to sodium acetate trihydrate. Patent Literature 4 further describes that the supercooled state of this heat storage material composition can be stabilized in a low-temperature environment of −13° C. or lower.